Concentric spool valve

ABSTRACT

A device which compares the position of concentric spools which normally move in unison. Any disagreement in the relative position of the spool positions above a predetermined amount uncovers a flow port which results in a hydraeric signal being generated to indicate the disagreement.

United States Patent Richard K. Mason Granada Hills, Calif.

lnventor Appl. No.-

Filed Patented Assignee June 13, 1969 Jan. 5, 1971 Bell AerospaceCorporation a corporation of Delaware CONCENTRIC SPOOL VALVE 12 Claims,5 Drawing Figs.

11.8. 137/553, 91/5i,9l/461,137/85,l37/625.62,137/625.69, 137/596 int.Cl. ..F16k 37/00, Fi6k 1 1/07 Field of Search 137/82- PrimaryExaminer-Henry T. Klinksiek Attorney-Nilsson, Robbins, Wells & BerlinerABSTRACT: A device which compares the position of concentric spoolswhich normally move in unison. Any disagreement in the relative positionof the spool positions above a predetermined amount uncovers a flow portwhich results in a hydraeric signal being generated to indicate thedisagreement.

2 a2 64 26 11a I00 ea 2 urea/us x l 60 SIGNAL 70 no u 42 74 72 /8 l 4090 l l 30 I04 9 6 a, N, 4, 0, 1,, Mom/foe I02 I 3/3534;- /2 48 pm, 6 24Inna F -/25 J A /22 I 12/ I4 I40 mama/ac SIGNAL LOAD 'lo CONCENTRICSPOOL VALVE BACKGROUND OF THE INVENTION l. Field of the Invention Thefields of art to which the invention pertains include the fields offluid handling, valve and valve actuation.

2. Description of the Prior Art.

The term hydraeric as used throughout the specification and claims isintended to be generic to fluid under pressure and includes bothhydraulics and prieumatics; As is well known in the prior art, redundantcontrol systems typically include a plurality of control channelsinterconnected from an input signal source to an output-load which iscontrolled by the system. The control channels are operative in such amanner that inthe event of a failure of one or more of the channels,such failure is detected and a shutoff portion of the system isactivated in order to'deactivate the failed channel. A hydraeric signalis generated which may be utilized to effect a transfer from the failedportion of the system to a duplicate, operable portion of the system,thus enabling the overall control system to continue to operateirrespective of the failed component. Alternatively, in the event of thefailure of a sufficient number of control channels, the hydraeric signalcan effect a' transfer to a manual mode of operation. 7

Such redundant control systems are particularly important in controllingthe multiple control surfaces on aircraft, and particularly with respectto the present generation aircraft of the supersonic or subsonic typeembodying control surfaces which experience heavy loads and require theutilization of power to effectproper control. Sincepower assist isnecessary with respect'to such aircraft, it is also necessary to detectfailures which may occur at any-point throughout the control system andto quickly eliminate such failures thereby to preclude damage to theaircraft. As exemplary of present redundant systems, see US, Pat. No.3,257,91 l to K.D. Garnjost et al. In suchfailure-detection,systems,spool positions must beconverted to hydraeric pressure pressureconverted to force, force compared to corresponding force from othervalves, the disparity converted to a valve motion, the valve to ahydraeric pressure, the pressure to a force and the force again to amotion. Each of these conversions requires a time delay and thecomplexity of construction of such a system makes it relativelyexpensive to manufacture and maintain.

SUMMARY OF THE INVENTION fecting a'desired system change upon failureinvolves the provision of a bore within the control valve spool and amonitor spool concentrically disposed in .the bore. lndependent meansare provided for positioning the, monitor spool and for moving themonitor and control spools in substantial unity. When an error is abovea predetermined value, the spools will move in relation to each other toeffect a hydraeric signal of the failure.

In particular embodiments, the monitor and control spools are controlledby hydraeric pressuredifferentials across each spool, each differentialbeing controlled by separate torque motors and associated flappervalves. Hydraeric pressure is provided in the control valve spoolbore'and a system return is spool within the control valve spool boreand a bore is defined through the land whereby hydraeric pressure onboth sides thereof are equalized. Upon relative movement of the monitorand control valve spools, the piston bore effects venting to the returnof the control valve spool bore. In one embodiment, a hydraeric path tothe control valve spool is in communication with a separate shutoffvalve for the system and effects the application of opposite electricalsignals to the torque motors to thereby latch the system in anovertravel position. In another embodiment, initial relativedisplacement of the monitor and control valve spools causes ventingthrough the monitor spool land bore to effect the application ofopposite hydraeric pressure differentials to the monitor and controlvalve spools to thereby latch the system in an overtravel position.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of avalve constructed in accordance with an embodiment of this invention;

FIG. 2 is a schematic diagram illustrating a portion of the structure ofFIG. 1 in a shutoff position;

FIG. 3 isa schematic diagram illustrating a portion of the structure ofFIG. 1 utilized to effect a'delay in electrical activation at startup;

FIG. 4 is a schematic diagram of a valve constructed in accordance withanother embodiment of this invention; and

FIG. 5 is a schematic diagram illustrating a portion of the structure ofFIG. 4 in larger view.

DETAILED DESCRIPTION Referring to FIG. 1, there is illustratedschematically a concentric spool comparator servovalve 10 forcontrolling the flow of hydraeric fluid through output controlpassageways l2 and 14 to thereby control aload 16.'The servovalve 10 canbe briefly described as a two-stage servovalve, the second stageincluding two spools l8 and 20 concentrically disposed, one in theother. An input signal is independently applied to separate torquemotors 22 and 24, controlling the movement of the concentric spools 18and 20, respectively, via first stage valves such as flapper valves 26and 30, respectively. During normal operation, the input signals areidentical and the spools l8 and 20 are in identical positions, i.e.,they do not move relative to each other. When an error is above apredetermined value, the spools 1 8 and 20 move in relation to eachother. This relative displacement of the concentric spools 18 and 20causes a drop in hydraeric pressure to a shutoff valve 34 to (a) actuatea pressure switch 36 to thereby cause appropriate opposite electricalhard-over signals to be applied to the torque motors 22 and 24 forlocking the mechanism; (b) vent a hydraeric signal port 38 to informlogic elements of the failure; and (c) shutoff flow to the controlpassageways 12 and 14 while simultaneously connecting them together.

Referring to the drawing in more detail, the concentric spools includean outer control valve spool 18 and an inner monitor spool 20. A housingis provided defining a bore 42 therewithin in which the control valvespool 18 is slideably disposed. The housing 40 defines a pari ofpassageways and 46 which are connected by means of passageways 48 and 50through the shutoff valve 34 to the output passageways 12 and 14. Theoutput passageways 12 and 14 are in communication with the chamber 52 ofan actuator cylinder 54 on opposite sides of an actuator piston 56therein to effect movement of the actuator rod 58 to position the load16, as is well known in the prior art.

A source 60 of hydraeric fluid is provided in communication with anetwork of passageways defined by the housing 40 to conduct thehydraeric fluid to' the ends of the concentric spools l8 and 20 tothereby provide means for establishing differential pressures across thespools and a system return 62 is provided therefor. As shown, hydraericfluid from the source 60 is conducted through a passageway 64 andbranches thereof, through fixed restrictions 68 and 70 to opposite sidesof the inner, monitor control spool 20. The hydraeric fluid is alsoconducted to the oppositely disposed nozzles 72 and 74 of the monitorspool flapper valve 30. Branch passageways are provided from thepassageway 64 to feed hydraeric fluid through restrictions 80 and 82 tothe opposite sides of the control valve spool 18 and to the oppositelydisposed nozzles 84 and 86 of the flapper valve 26 which is utilized tocontrol the movement of the control valve spool 18. I-Iydraeric fluidfrom the source 60 is also fed through a branch passageway andrestriction 88, via openings 90 in the control valve spool through apassageway 94 to the shutoff valve 34 for purposes hereinafterdescribed. Another passageway 96 feeds hydraeric fluid from thepassageway 64 through a port 98 in the shutoff valve to the hydraericsignalport 38.

The system return 62 is connected via a return passageway 100 to acommon return chamber 102 utilized for both flapper valves'26 and 30.

The outer, control valve spool 18 is formed with a bore 104longitudinally therethrough through which the inner, monitor .valve 20extends. The control valve spool 18 is provided centrally with a port106 which during normal operation is :blocked by a central land 108 onthe monitor spool 20. The central land 108 defines a passageway 110therethrough for establishing open communication between opposite sidesthereof, and this passageway 110 vents return totthe bore 104irrespective of the translationdirection of the spools l8 and A feedbackelement 112 is connected between the flapper of the control spool torquemotor 22 and the central region of the control valve spool 18, toprovide feedback effect, as is well known to the prior art (see US. Pat.No. 2,947,286). A feedback element 114 extends through the control valvespool central port 106 into a central portion of the monitor spool toprovide position feedback to the monitor spool torque motor 24.

With respect to control operation, hydraeric fluid is fed from thesource 60 through the passageway 64 and branches and restrictionspreviously described to the nozzles and the ends of the control andmonitor spools 18 and 20. Since the reaction areas of these second stagespools are different, the restriction pairs 68, 70 and 80, 82 are sizedso'that the first stage flow gains are appropriately proportional toachieve identical movement of the spools 18 and 20 responsive todifferential pressure signals generated by the nozzle-flapper firststages upon receipt of identical signals by the respective torque motors22 and 24.

The fluid-metering function is accomplished only by the control valvespool 18, that is, it is only through movement of the control valvespool 18 within the bore 42 that fluid flow through passageways 44 and46 is metered. Movement of the control valve spool 18 to the left, withrespect to the drawing, exposes the left side passageway 44 to hydraericfluid from the source 60 by means of a branch passageway connecting tothe passageway 64 as shown. At the same time, the right side passageway46 is directly exposed to the system return 62 by opening intocommunication with the return chamber 102 associated with the flappervalves 26 and 30. Accordingly, upon leftward movement of the controlvalve spool 18 with respect to the housing 40, hydraeric fluid from thesource 60 is fed through the passageway 48, through the shutoff valve 34to the actuator passageway 12, and from there to the left side of theactuator piston 56. The right side of the actuator piston 56 is exposedto the system return through the right side actuator passageway 14.through the shutoff valve 34, and via the passageway 50 to thepassageway 46. Rightward movement of the control spool 18, with respectto the housing 40, operates in a symmetrical manner to direct hydraericfluid from the source 60 to the right side of the actuator piston 56 andto connect to the left side thereof to the system return. During suchoperation, the monitor spool 20 substantially follows each movement ofthe control valve spool 18.

With respect to failure detection operation, it will be seen thatrelative movement between the control and monitor spools 18 and 20results in exposure of one side or the other of the monitor spoolcentral land 108 to the system return by communication thereof with thesystem return chamber 102, and this venting to return is effected to theother side of the land 108 by means of the passageway therethrough.Accordingly, the annular space 118 on the right side of the monitorspool land 108 is vented to return regardless of the direction of therelative movement between the control and monitor spools 18 and 20. Thisresults in venting to return of the shutoff valve 34 through thepassageway 94.

The shutoff valve 34 includes a housing portion 120 which defines acentral bore 122 lengthwise therein in which a spool 124 is positionedfor selectively covering and uncovering various ports defined by thehousing thereby to shut off operation of the actuator valve 54. A spring126 is positioned between the left side of the shutoff valve bore 122and the end of the spool 124. The spring 126 is compressed by extremeleftward movement of the spool 124 therein. The spool 124 is maintainedin the extreme leftward position during normal operation of theservovalve 10 by means of hydraeric fluid form the source 60 beingapplied to a right side land 128 of the spool via the passageway 94thereto and the venting to system return 62 of the opposite side of aleft side 129.

Upon relative movement between the control and monitor spools 18 and 20,the annular space 118 is vented as described above to thereby vent theshutoff valve passageway 94, so that there is a pressure drop in thechamber 131 on the right side of the land 128 of the shutoff valve spool124. This venting allows the force of the spring 126 to move the shutoffvalve spool 124 to the right as viewed in FIG. 1.

Referring to FIG. 2, the shutoff valve 34 is shown following translationof the spool 124 as above described. It will be seen that the outputpassageways 12 and 14 are connected together thereby equalizing pressurein each side of piston 56. Lands and 132 on the shutoff valve spool 124close off communication between the load passageways 12 and 14 and theirrespective feeding passageways 48 and 50. Furthermore, another land 134on the shutoff valve spool 124, is moved into position to block flow ofhydraeric fluid from the pressure passageway 96. Simultaneously,movement of the right side land 123 opens communication, via a port 136,between the now-vented-to-return passageway 94 and the hydraeric signalport 38. Such venting effects a sudden change in hydraeric signal toinform logic elements of the detected failure, as well known to theprior art.

Simultaneously with the foregoing shutoff valve movements, the ventingto return of the passageway 94 effects the closing of the pressureswitch 36 via a passageway 138 between the pressure switch 36 and thechamber 131. Referring additionally to FIG. 1, the pressure switch 36 isthere shown in an open position wherein hydraeric fluid fed from thepassageway 64 via the passageway 94 is applied against a piston 140within the pressure switch 36 to force the piston 140 against the returnforce of a spring 142 therein so as to prevent the piston 140 fromeffecting electrical contact between electrical leads 144 and 146. Asillustrated in FIG. 2, upon venting to return through the passageway138, spring 142 translates the piston 140 toward the left and intocontact with the electrical leads 144 and 146 thereby electricallyconnecting them together.

Any other pressure switch means known to the art can be utilized, theeffect being to cause electrical current to be supplied from a sourcethereof, shown as a battery via the electrical leads 144 and 146,interconnected by piston 140, and electrical lead 148 connected to adouble pole solenoid switch 150 to energize the same. Prior toactivation of the solenoid switch 150, the two torque motors 22 and 24received identical electrical signals for operation thereof from acontrol spool signal generator 152 and a monitor spool signal generator154. However, upon activation of the solenoid switch 150, both torquemotors 22 and 24 are caused to receive latching signals from a latchingsignal generator 156. The latching signal generator 156 receivesfeedback signals, as indicated by the arrow 158, from the servovalve 10relating the offcenter position of each of the second stage spools 18and 20 and generates opposite polarity electrical and hard-- 1 oversignals to the. torque motors 22' and 24 to thereby cause the monitorand control spools to assume opposite extreme positions to'thereby latchthe spools in an overtravel position. Any of a variety of means known tothe art can be utilized to relate the offcenter directions of the,second stage spools; for

example, nozzle'pressure detectors can be utilized. Since the pressureswitch 36 will effect latching signals, as above. in the absence ofhydraeric pressure, means must be Briefly, the passageways are disposedso that first stage flow of hydraeric fluid from flapper valve 226 goesdirectly to the provided duringinitialpressurization ofthe system todisconnect the pressure switch 36 so asto'lallow pressure equilibrium tobeobtained without latching. Any of a variety of delay devices knowntothe'art may be utilized. Referring to FIG 3, a delay device 160 isshown in anopen position, prior to initial.

pressurization. The delay? device includes a housing 162,

' which defines a bore 164 therein, and a piston 166 slideably ,ends ofthe control spool 218. The first stage flow for the monitor spool 220must go through the control valve spool 218 and this is accomplished bydirecting the fluid flow spool 218. The hydraeric fluid is alsoconducted to the opdisposedinthe. bore 164 abutting a return spring 168.Upon pressurization, hydraeric fluidfrorn' the source 60 is fed into thepassageway '64 via inlet and outlet ports" 170 and 172, respectively,through the delay-device housing 162. An exhaust line 174 is connectedto the return 62 (FIG. 1) through a restriction 176. Uponpressurization, the delay piston,l66 is caused by the hydraeric pressureto move against the return spring 158 to effect contact betweenelectrical leads 146 and I 148 disposed within the housing. However, theexhaust restriction 176 is sized so as to delay translation of the delaypiston 166 for a period of timev sufficient to allow the remainder ofthe'system to obtain pressure equilibrium.

Referring now to FIG. 4, there is'illustrated schematically a concentricspool comparator servovalve 210 constructed in accordance withanotherembodiment of this invention and utilizedfor controlling the flowof hydraeric fluid through output passageways 212 and 214 to therebycontrol a load 216. This servovalve 210 is similar tothe servovalvedescribed above'with respect to FIGS. .1'3 in that it can be describedas a two-stage servovalve with the second stage including spools 2 18and 220 concentrically disposed, one in the other. Here too, an inputsignal is. independently applied to. separate torque motors 222 and 224which control the movementqof the concentric spool218 and 220 via firststage flapper valves i 226 and 230. Duririg normal operation, the inputsignals are identical and, the second stage spools 218 and 220 are inidentical position s. When an error is abovea predetermined value, thespools 218 and 220 will move in relation to each other. This relativedisplacement of the concentric spools 218 and 220 will automaticallycause a pressure differential to be applied across the inner monitorspool 220 in such direction as positely disposed nozzles 284 and 286 ofthe flapper valve 226 which is utilized to control the movement of thecontrol valve spool 218. Branch passageways are provided from thepassageway 264 to feed hydraeric fluid through restrictions 258 and 270to the oppositely disposed nozzles 272 and 274 of the monitor spoolflapper valve 230. This hydraeric fluid is also conducted through ports273 and 275 in the control spool 218 into annular spaces 277 and 279defined between pairs of lands 281, 283 and 285, 287 respectivelydisposed on opposite ends of the monitor spool 220. From there, thehydraeric fluid flows through passageways 289 and 291, defined by theend Referring to FIG. 5 and to P16. 4 in more detail, a housing 240 isprovided defining a bore therein in which the control spool 218 isslideably disposedJTlie housing 240 defines apair of passageways 244 and246 which are connected by means of the aforenotedoutput passageways 212and 214, respectively, to the chamber 252 of an actuator cylinder 254 onopposite sides of a piston 256 carried on an actuator rod 258. Movementof the actuator rod 258 to position the load 216 is effected andcontrolled by selectively pressurizing one of the output passageways 212and 214 while exposing the other of the passageways to the return.

A source 260' of hydraeric fluid is provided in communication with anetwork of passageways defined by the housing 240 to conduct thehydraeric fluid to the ends of the concentric spools 218 and 220to-thereby establish differential pressures across the spools,and asystem return 262 is provided therefor.

lands 281 and 285, respectively, to the ends of the monitor spool 220.Sealed cavities are formed at the ends of the monitor spool except forcommunication through the passageways 289 and 291.

Hydraeric fluid flows from the source 260 through a branch 265 andsubbranches 267 and 269 to oppositely disposed ports 293 and 295,respectively, through the control spool 218. With respect to the lefthand side, in the drawing, of the control spool 218, the port 295thereat is utilized only for purposes of failure detection, as willhereinafter be described. With respect to the right hand side of thecontrol spool 218, the port 293 thereat is utilized (a) for latchingupon failure (b) to supply hydraeric fluid to the hydraeric signalpassageway 238, and (c) to supply hydraeric fluid for the meteringfunction of the control spool 218.

The system return 262 is connected via a return passageway 300 to acommon return chamber 302 utilized for both flapper valves 226 and 230.A system return 262 is also connected via a return passageway 301 andbranch 303 to ports 305 and 307, respectively, through opposite endportions of the control valve spool 218. The return ports 305 and 307are closed during normal operation by the monitor spool end lands 281and 285, respectively, but one or the other of the ports 305 and 307 areexposed into communication with the relevent land passageway 289 and 291when the spools 218 and 220 are in relative displacement, so as tofacilitate latching into an overtravel position, as hereinafterdescribed. The control valve spool 218 is provided centrally with a port306 whereby its bore 304 can communicate with the flapper return chamber302; however, during normal operation the port 306 is blocked by monitorspool land'308 and 309 on opposite sides thereof. 1

A feedback element 312 is connected between the flapper of the controlvalve spool torque motor 322 and the central region of '.the controlspool 218 and a feedback element 314 extends through the controlvalvespool central bore 306 into a central portion of the monitor spool 220to provide position feedback to the monitor spool torque motor 224.

With respect to control operation, hydraeric fluid is fed from thesource 260 through the passageway 265 and branch 267 into the controlvalve spool bore 304 via the right side port 293 therethrough. Fromthere, the hydraeric fluid feeds via a port 311 in the control valvespool to the hydraeric signal passageway 238 and to a bridgingpassageway 313 (both shown in shadow in HQ 2). Reduced diameter portions315 and 317 are formed in the outer surface of the control valve spool218 for communication with the passageways 244 and 246. The bridgingpassageway 313 enables the provision of hydraeric fluid supply ports 319and 321 adjacent the reduced diameter portions 315 and 317 communicateswith a hydraeric supply port 319 or 321 the thereby supply hydraericfluid to the passageway 244 or 246. Simultaneously therewith, the otherreduced diameter position is exposed to the system return 262 by openinginto communication with the return chamber 302. Accordingly, uponleftward movement of the control valve spool 218 with respect to thehousing 240, hydraeric fluid from the source 260 is fed through thepassageway 265, through the branch passageway 267, through the controlvalve spool port 293 into the control valve spool bore 304. out of thebore 304 through the control valve spool port 311, through the bridgingpassageway 313, into the supply port 319, into the left side reduceddiameter portion 315, and from there into the left side passageway 244.The right side reduced diameter portion 317 is simultaneously exposed tothe return chamber 302, thereby exposing the right side passageway 246to return. Rightward movement of the control spool 218, with respect tothe housing, operates in a symmetrical manner to direct hydraeric fluidfrom the source 260 to the right side passageway 246 and to connect theleft side passageway 244 to the system return.

With respect to movement in unison of the control spool 218 and themonitor spool 220, hydraeric fluid is fed from the source 260 throughthe passageway 264 and restrictions 280 and 282 to the ends of thecontrol valve spool 218, and hydraeric fluid is also fed from thepassageway 264 through the restrictions 268 and 270 through ports 273and 275 in the control valve spool 218 leading to the annular spaces 277and 279, respectively, as described above and, from there, through thepassageways 289 and 291, respectively, to the ends of the monitor spool220. Since the reaction areas of the second stage spools 218 and 220 aredifferent, the restriction pairs 268, 270 and 280, 282 are sized so thatthe first stage flow gains are appropriately proportional. Identicalmovement of the spools 218 and 220 is thereby effected upon receipt ofidentical signals by the respective torque motors 222 and 224.

With respect to failure detection and latching operation, it will beseen that relative movement between the control and monitor spools 218and 220 results in exposure of one or the other of the passageways 289and 291 to a system return passageway 301 or 303 to expose that end ofthe monitor spool to return 262. The other passageway is simultaneouslyexposed to hydraeric fluid from the passageway 265 or branch 267 tothereby conduct hydraeric fluid from the source 260 to the opposite endof the monitor spool 220. The result is that a large differentialpressure is effected across the monitor spool 220 to further move themonitor spool 220 within the control spool bore 304 in the samedirection as the initial error detecting relative movement. In otherwords, if the error or failure caused relative movement of the monitorspool 220 to the left of the control valve spool 218, the passageway 239on the left side of the monitor spool communicates with the return line301 to expose that end of the monitor spool to the system return 262 andthe passageway 291 at the other end of the monitor spool exposes thatend of the monitor spool to hydraeric fluid from the passageway 267. Theresultant differential effects further leftward movement of the monitorspool 220 within the control valve spool bore 304 until the left end ofthe monitor spool 220 contacts the inner left surface of the controlspool 218. Rightw'ard movement of the monitor spool 220 relative to thecontrol valve spool 218 operates in a symmetrical manner to further movethe monitor spool 220 within the control spool 218 to abut that end ofthe monitor spool against the right side of the control spool 218. Ineither case, the spools are effectively latched into an overtravelposition.

Relative movement of the spools also effect a venting of the passageways244 and 246 and of the hydraeric signal passageway 238. Venting of thehydraeric signal passageway 238 is accomplished by means ofa vent port316 into the bore 304, which vent port 316 is in communication with thereturn chamber 302 via a passageway 318 (shown in shadow in FIG. 5). Aland 320 on the monitor spool 220 covers the vent port 316, but uponrelative movement of the spools, the vent port 316 exposes the controlspool bore 304 to return and via the control valve spool bore 311, ventsthe hydraeric signal passageway 238 to return tothereby signal failureto'logic units in the system.

By the same means, the bridging passageway 313 is vented. Accordingly,if the monitor spool 220has moved to the right relative to the controlvalve spool 218,.the monitor spool lands 308 and 309 move to expose theleft side passageway 244 to the system return 262 via the bridgingpassageway 313 and simultaneously the right side passageway 246 isexposed directly to the system return chamber 302. Leftward movement ofthe monitor spool 220 relative to the control valve spool 218 operatesin a symmetrical manner tovent the right side passageway 246 to thebridging passageway 313 and the left side passageway 244 directly to thereturn chamber 302. In either case, both actuator passageways 244 and246 are vented to the system return. I

The servovalve 210 can be unlocked from a failed position by means of afour-way solenoid valve such as depicted at 322. Such four-way solenoidvalves are well known to the art and in this embodiment serve to reversethe pressure and return system ports to unlatch the valve and force themonitor and control spools to an operative position.

lclaim:

1. in a hydraeric control system for applying hydraeric fluid from asource thereof to a load through ports controlled by a control valvespool, and including a mechanism for effecting a desired system changeupon failure, the improvement wherein a bore is defined by said controlvalve spool and said mechanism comprises:

a monitor spool slideably disposed in said bore;

independent means for positioning said monitor spool;

means for moving monitor spool and control spool in substantial unity;and

means for detecting relative movement between said control spool andsaid monitor spool.

2. The improvement of claim 1 including means for applying a hydraericpressure differential across said control valve spool and means forapplying a hydraeric pressure differential across said monitor spool inproportion to said control valve spool hydraeric differential.

3. The improvement of claim 1 including a hydraeric path through saidcontrol valve spool, said monitor spool and control valve spool beingformed so that said relative movement causes a change in hydraericpressure in said path to thereby effect a change in said system.

4. The improvement of claim 1 including a hydraeric path through saidcontrol valve spool and a system return, said monitor spool and controlvalve spool being formed so that said relative movement vents said pathto said return to thereby effect a change in said system.

5. The improvement of claim 1 including a hydraeric path into saidcontrol valve spool bore and a system return in communication with saidcontrol valve spool bore, said monitor spool and control valve spoolbeing fonned so that said relative movement effects the venting of saidhydraeric path to said return to thereby effect a change in said system.

6. The improvement of claim 5 including a shutoff valve for said systemin communication with said hydraeric path and operative upon venting ofsaid hydraeric path to shut off said load from said hydraeric fluidsource.

7. The improvement of claim 5 including means responsive to a hydraericpressure drop for signaling failure of said system, said pressureresponsive means bei'ng in operative communication with said hydraericpath.

8. The improvement of claim 2 including a hydraeric path and a systemreturn path to each end of said monitor spool, said monitor spool andcontrol valve spool being formed so that upon said relative movementcommunication is effected the other end of said monitor spool and saidhydraeric path to thereby latch said system in an overtravel position.

9. The improvement of claim 2 including first and second meansresponsive to electrical signals for controlling the hydraeric pressuredifferentials to said monitor spool and control valve spool,respectively, wherein substantially identical linear movements of saidmonitor and control spools are normally effected by identical electricalsignals to said first and second means.

l0. The improvement of claim 9 including means responsive to saidrelative movement to effect the application of opposite electricalsignals to said first and second means to thereby latch said system inan overtravel position.

11. The improvement of claim 2 including a land on said monitor spoolwithin said $11331 spool bore and a bore defined through said land incommunication with said control valve spool bore whereby hydraericpressure on both sides of said land are equalized, said monitor spooland control valve spool being formed so that said land bore effects achange in hydraeric pressure within said control valve spool bore uponsaid relative movement of said monitor and control spools.

12. A redundant control systemcomprising a plurality of controlchannels, each control channel including a control member and a monitormember, means for effecting substantially identical movements of saidcontrol and monitor members and means responsive to adifferential insaid movements to disable that channel independently of the others ofsaid plurality of control channels. a

1. In A hydraeric control system for applying hydraeric fluid from asource thereof to a load through ports controlled by a control valvespool, and including a mechanism for effecting a desired system changeupon failure, the improvement wherein a bore is defined by said controlvalve spool and said mechanism comprises: a monitor spool slideablydisposed in said bore; independent means for positioning said monitorspool; means for moving monitor spool and control spool in substantialunity; and means for detecting relative movement between said controlspool and said monitor spool.
 2. The improvement of claim 1 includingmeans for applying a hydraeric pressure differential across said controlvalve spool and means for applying a hydraeric pressure differentialacross said monitor spool in proportion to said control valve spoolhydraeric differential.
 3. The improvement of claim 1 including ahydraeric path through said control valve spool, said monitor spool andcontrol valve spool being formed so that said relative movement causes achange in hydraeric pressure in said path to thereby effect a change insaid system.
 4. The improvement of claim 1 including a hydraeric paththrough said control valve spool and a system return, said monitor spooland control valve spool being formed so that said relative movementvents said path to said return to thereby effect a change in saidsystem.
 5. The improvement of claim 1 including a hydraeric path intosaid control valve spool bore and a system return in communication withsaid control valve spool bore, said monitor spool and control valvespool being formed so that said relative movement effects the venting ofsaid hydraeric path to said return to thereby effect a change in saidsystem.
 6. The improvement of claim 5 including a shutoff valve for saidsystem in communication with said hydraeric path and operative uponventing of said hydraeric path to shut off said load from said hydraericfluid source.
 7. The improvement of claim 5 including means responsiveto a hydraeric pressure drop for signaling failure of said system, saidpressure responsive means being in operative communication with saidhydraeric path.
 8. The improvement of claim 2 including a hydraeric pathand a system return path to each end of said monitor spool, said monitorspool and control valve spool being formed so that upon said relativemovement communication is effected between that end of said monitorspool in the direction of its relative movement and said system returnpath and between the other end of said monitor spool and said hydraericpath to thereby latch said system in an overtravel position.
 9. Theimprovement of claim 2 including first and second means responsive toelectrical signals for controlling the hydraeric pressure differentialsto said monitor spool and control valve spool, respectively, whereinsubstantially identical linear movements of said monitor and controlspools are normally effected by identical electrical signals to saidfirst and second means.
 10. The improvement of claim 9 including meansresponsive to said relative movement to effect the application ofopposite electrical signals to said first and second means to therebylatch said system in an overtravel position.
 11. The improvement ofclaim 2 including a land on said monitor spool within said control spoolbore and a bore defined through said land in communication with saidcontrol valve spool bore whereby hydraeric pressure on both sides ofsaid land are equalized, said monitor spool and control valve spoolbeing formed so that said land bore effects a change in hydraericpressure within said control valve spool bore upon said relativemovement of said monitor and control spools.
 12. A redundant controlsystem comprising a plurality of control channels, each control channelincluding a control member and a monitor member, means for effectingsubstantially identical movements of said control and monitor membersAnd means responsive to a differential in said movements to disable thatchannel independently of the others of said plurality of controlchannels.